Method and apparatus for automatic detection and healing of signal pair crossover on a high performance serial bus

ABSTRACT

An automatic crossover and healing process is disclosed for the P1394b standard. In particular, a crossover process is disclosed which comprises coupling the transmitting logic of a PHY to TPA, and coupling the receive logic of a PHY to TPB.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to co-ownedU.S. patent application Ser. No. 11/139,815 entitled “Method andApparatus For Automatic Detection and Healing of Signal Pair CrossoverOn A High Performance Serial Bus” filed May 27, 2005 now U.S. Pat. No.7,401,173, which is a Continuation of U.S. patent application Ser. No.10/464,169, filed Jun. 17, 2003, now issued as U.S. Pat. No. 6,944,705,which is a Continuation of U.S. patent application Ser. No. 09/557,073,filed Apr. 21, 2000, now issued as U.S. Pat. No. 6,618,785, the entiretyof each of the foregoing being incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to data communications. In particular, thepresent invention relates to automatic detection of signal paircrossover on a high performance serial bus system.

2. The Prior Art

BACKGROUND

The IEEE 1394-1995 standard has revolutionized the consumer electronicsindustry by providing a serial bus management system that featured highspeeds and the ability to “hot” connect equipment to the bus; that is,the ability to connect equipment without first turning off the existingconnected equipment. Since its adoption, the IEEE 1394-1995 standard hasbegun to see acceptance in the marketplace with many major electronicsand computer manufacturers providing IEEE 1394-1995 connections onequipment that they sell.

However, as technologies improved, the need to update the IEEE 1394-1995standard became apparent. A new standard is being proposed at the timeof the filing of this application, herein referred to as the P1394bstandard. Improvements such as higher speeds and longer connection pathswill be provided. It is contemplated at the time of this filing thatcable lengths of up to 100 meters may be possible using the P1394bstandard. Furthermore, the connections between 1394 devices may beestablished using wiring previously installed in buildings compliantwith appropriate regulatory codes.

In the discussion that follows, it will be necessary to distinguishbetween the various standards that are being proposed as of the date ofthis application. Additionally, it will be necessary to distinguishhardware and packet transmissions that are compatible with the P1394bstandard and not earlier standards.

Thus, the term “Legacy” will be used herein to refer to the IEEE1394-1995 standard and all supplements thereof prior to the P1394bstandard. Thus, for example, a Legacy node refers to a node compatiblewith the IEEE 1394-1995 standard and all supplements thereof up to, butnot including, the P1394b standard.

Furthermore, in the discussion that follows cable physical layers (PHYs)that are compatible with the P1394b standard may be referred to invarious ways, depending upon the context the PHY is operating in and thecapability of the PHY. For example, a PHY that has circuitry compatiblewith the P1394b standard but not any previous standards will be referredto as a B only PHY. Also, a PHY that is compatible with both the P1394bstandard and all predecessors and is communicating with only devicescompatible with the P1394b standard will be referred to as B PHYs.Finally, a PHY that is communicating with both Legacy devices anddevices compatible with the P1394b standard will be referred to as aborder device, border PHY, or border node. Finally, a communicationssystem that has only B PHYs attached will be referred to as a B bus.

P1394b Cabling

FIG. 1 shows a prior art diagram of a cable 100 according to the P1394bstandard. Cable 100 includes a first signal pair 105 covered by a shield106, a second signal pair 107 covered by a shield 108, and a power pair104. The pairs are then enclosed in an outer shield 102, and extruded inan outer jacket 101.

According to the P1394b standard, the first and second signal pairs 105and 107 form a differential pair, with different information beingtransmitted through each signal pair. As is appreciated by those ofordinary skill in the art, when a cable is connected to P1394b-compliantdevice, the device will receive information on a signal pair designatedas twisted pair A (TPA), and will transmit on a signal pair designatedas twisted pair B (TPB).

FIG. 2 shows a diagram of a prior art P1394b connection. FIG. 2 includesa PHY 1 having a connection point TPA and TPB, and a PHY 2 having aconnection point TPA and TPB. Together, a TPA and TPB pair comprises aport. PHYs 1 and 2 are connected via cable 200, which has a first signalpair 202 and a second signal pair 204.

As can be seen by inspection of FIG. 2, because the PHYs transmit andreceive on different signal pairs, the first and second signal pairsmust be “crossed-over” to properly couple the PHYs. Thus, in FIG. 2,first signal pair 202 is connected to PHY 2's TPB and must becrossed-over to be connected to PHY 1's TPA. The same is true for secondsignal pair 204. As is appreciated by those of ordinary skill in theart, the signal pair crossover is typically accomplished within theP1394b cabling itself.

In P1394b, a PHY engages in simultaneous transmission and receptioncalled ‘dual sirnplex’. This is different from Legacy, which transmitsdata on TPB and a “strobe” signal on TPA. Its peer port receives thedata on TPA and the strobe on TPB. Legacy operates in “half duplex”,whereby previous arbitration determines the direction of the data flowon any given connection. The two connected ports then prime themselvesso that one port transmits and one port receives as described above.Because of the strobe signal, Legacy operation requires the use of acrossover, and there is no possibility for operation if the crossover isnot provided. To facilitate backwards compatibility, P1394b specifiesthat the port transmits on TPB and receives on TPA.

FIG. 3 is a diagram of a prior art P1394b system. Where similardesignations are used herein, they are intended to refer tosubstantially similar matter. FIG. 3 shows what is referred to as a“cluster” of PHYs 1, 2, and 3. The PHYs may represent P1394b-compliantdevices such as a computer, video camera, and a mass storage device. InFIG. 3, the PHYs are each connected to each other by a cable 200 in apoint-to-point fashion to form the cluster. When devices are connectedas in FIG. 3, the crossover normally provided in the cabling issufficient to provide a proper connection for P1394b devices.

However, one of the advantages of the P1394b standard is the ability torun long lengths of cable (as far as 100 m) and connect P1394b devicesthroughout a house which has pre-existing wiring, for example. Thisleads to the problem illustrated in the diagram of FIG. 4.

FIG. 4 shows PHY 1 connected to PHY 2, through a wall connection. As isknown by those of ordinary skill in the art, when a house is wired forpoint-to-point connections through a wall, typically wiring is used thatwill not implement a crossover. FIG. 4 shows such a straight-throughwire 400 having conductors 402 and 404 which are not crossed-overinternally, and external wall connections pairs 406 and 408.

As can be seen by inspection of FIG. 4, if a user attempts to connectPHY 1 to PHY 2 using a cable such as straight-through cable 400, theTPB1 will be coupled to TPB2 through the wall connection as shown withthe solid black conductor, and TPA1 will be coupled to TPA2 as shownwith the dashed conductor path. As is appreciated by those of ordinaryskill in the art, such a connection will not function properly, and PHY1 will not communicate properly with PHY 2.

To solve the problem of FIG. 4, two types of patch cords are used whichare commonly available. One patch cord implements the crossover and onedoes not. This solution is tolerable in commercial buildings, whereprofessional network managers ensure that the correct type of cable isused in each circumstance, and also where devices are typicallyconnected semi-permanently.

However, this situation of FIG. 4 leads to frustrating difficulties inthe consumer environment, where the subtleties of “cross-over” and“straight-through” patch cables are bewildering.

Furthermore, patch cords have certain drawbacks. For example, patchcords require much trial-and-error to locate and correct the connectionthat is not crossed-over, causing much user confusion and frustration.Furthermore, in modern homes and businesses which utilizeP1394b-compliant devices, often all devices are coupled to a centralrouter through in-wall wiring, making any troubleshooting effort evenmore difficult.

Hence, there is a need for a method and apparatus for automaticallyhealing a crossover problem in a P1394b-compliant system. Furthermore,there is a need for a method and apparatus for automatically healing acrossover in the P1394b environment without the need for different typesof patch cords.

BRIEF DESCRIPTION OF THE INVENTION

The present invention satisfies the foregoing needs by providing, interalia, methods and apparatus for automatic detection of signal paircrossover on a high performance serial bus system. In accordance with afirst aspect of the invention, a data communication apparatus isdisclosed. In one embodiment, the data communication apparatus includes:a transmit interface configured to transmit a first predetermined signalon power up; a receive interface configured to receive a secondpredetermined signal; the data communication apparatus configured toperform a crossover function if the receive interface does not receivethe second predetermined signal. In one variant, the crossover functionincludes: examining a random value, the random value being determined byan algorithm, and if the value of the random value meets a predeterminedcriterion, then: configuring the transmit interface to receive thesecond predetermined signal; and configuring the receive interface totransmit the first predetermined signal. In another embodiment, theapparatus includes a first interface configured to transmit at least afirst signal; a second interface configured to receive at least a secondsignal; and logic in signal communication with the first interface andthe second interface. In one variant, the logic is configured to: waitfor a predetermined period after transmission of the first signal; andcheck the second interface, after the predetermined period has expired,to determine if the second signal is received; and: if the second signalis received at the second interface, then attempt to form a network; andif the second signal is not received at the second interface, and thefirst or second interfaces are not in use at that time, then performingdetection of the second signal on the first interface. In yet anothervariant, the logic is configured to: check the second interface todetermine if the second signal is received; if the second signal isreceived at the second interface, attempt to form a network; and if thesecond signal is not received at the second interface, and one or moreof the first or second interfaces are in use at that time, then: (i)wait for a predetermined period; and (ii) after expiration of theperiod, perform detection of the second signal on the first interface.

In accordance with a second aspect of the invention, a communicationnetwork comprising at least two nodes and a communication bus isdisclosed. In one embodiment, the at least two nodes communicate witheach other over the communication bus without an intervening crossoverinterface; and at least one of the at least two nodes is configured fordetection and healing a crossover in communication. The detection andhealing includes: detecting an absence of a first signal; determiningwhether a signal interface of the at least one of the at least two nodesis generating a second signal; and responsive to a probabilisticfunction and the acts of detecting and determining, switching between atransmit port and a receive port. In one variant, the crossoverinterface includes a cable, and the at least two nodes comprise nodescompliant with IEEE Std.1394b. In a further variant, the first signalincludes a signal detect tone compliant with IEEE Std.1394b. In afurther variant, the probabilistic function includes a Boolean function.In a further variant, the probabilistic function is used by the at leasttwo nodes for root node decision. In a further variant, the detectionand healing further includes transmitting a predetermined number oftransmissions of a second signal.

In accordance with a third aspect of the invention, a communicationsystem is disclosed. In one embodiment, the communication systemincludes: an interface comprising a first communication path and asecond communication path; at least one node; the node including a logiccircuit comprising a receive circuit and a transmit circuit; wherein thetransmit circuit is connected to a first and a second communicationpaths via a first passgate and the receive circuit is connected to thefirst and the second communication paths via a second passgate. Thefirst passgate is utilized in combination with a crossover function andin response to a crossover enable signal, connects the transmit circuiteither to the first communication path or the second communication path.The second passgate is utilized in combination with the crossoverfunction and in response to the crossover enable signal, connects thereceive circuit either to the first communication path or the secondcommunication path A logical state of the crossover enable signal isresponsive to detection of a signal on the second communication path anda value of a first variable, the value of the first variable beingdetermined by an algorithm that is utilized for another purpose inaddition to the crossover function. In one variant, another purposeincludes resolving contention between the at least one node and one ormore other nodes of a network using a serialized bus protocol.

In accordance with a fourth aspect of the invention, a home networkcomprising at least two devices and a communication bus is disclosed. Inone embodiment, the communication bus includes a first signaltransmission path and a second signal transmission path; and at leastone of the at least two devices includes a physical layer configured todetect reception of a signal on the second signal transmission path; andif the physical layer has not received the signal, then responsive tothe lack of receipt of the signal examining a variable associated with arandomized function and implementing, by the physical layer, a crossoverprocess.

In accordance with a fifth aspect of the invention, a method of forminga network is disclosed. In one embodiment, the method includes:transmitting a first signal on a first interface; waiting for apredetermined period of time after completion of the transmitting;checking at a second interface, after the predetermined period of timeis over after the transmitting, if a second signal is received; and ifthe second signal is received at the second interface, then attemptingto form a network; and if the second signal is not received at thesecond interface, and the first signal is determined not to betransmitted on the first or second interface at that time, thenperforming detection of the second signal on the first interface.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a diagram of a prior art P1394b cable.

FIG. 2 is a diagram of a prior art P1394b connection.

FIG. 3 is a diagram of a prior art P1394b system.

FIG. 4 is a diagram of a prior art P1394b system.

FIG. 5 is a flowchart of a first aspect of a crossover process accordingto the present invention.

FIG. 6 is a flowchart of a second aspect of a crossover processaccording to the present invention.

FIG. 7 is a schematic of crossover circuitry according to the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Persons of ordinary skill in the art will realize that the followingdescription of the present invention is illustrative only and not in anyway limiting. Other embodiments of the invention will readily suggestthemselves to such skilled persons having the benefit of thisdisclosure.

The present invention relates to data communications. In particular, thepresent invention relates to automatic detection of signal paircrossover on a high performance serial bus system.

The invention further relates to machine readable media on which arestored embodiments of the present invention. It is contemplated that anymedia suitable for retrieving instructions is within the scope of thepresent invention. By way of example, such media may take the form ofmagnetic, optical, or semiconductor media.

The present invention relates to data structures and the transmission ofsuch data structures. It is contemplated that the present invention maybe embodied in various computer and machine readable data structure.Furthermore, it is contemplated that data structures embodying thepresent invention will be transmitted across computer and machinereadable media.

The present invention may be described through the use of flowcharts.Often, a single instance of an embodiment of the present invention willbe shown. As is appreciated by those of ordinary skill in the art,however, the protocols and procedures described herein may be repeatedcontinuously or as often as necessary to satisfy the needs describedherein. Accordingly, the representation of the present invention throughthe use of flowcharts should not be used to limit the scope of thepresent invention.

The present invention further relates to devices that embody the P1394bstandard. By way of example, such devices may include those typicallyused in an audio/video entertainment system, such as home theaterreceivers, DVD players, computers, or hand-held devices such as camerasand the like. The devices may also include those industrial in nature,such as test and measurement equipment, professional audio/videorecording devices, as well as system control or robotic devices found inan industrial environment.

The invention also relates to nodes and physical computers, such asstate machines. The present invention may be embodied in any collectionof nodes linked together through a bus. Typically, each device connectedto the bus will also have one corresponding node physical layercontroller embedded therein. However, a given device may have more thanone node, and therefore it follows that one device may have more thanone connection to more than one bus. For the discussion that follows,the examples will show the typical situation where one node correspondsto one device.

Each node may communicate to other nodes in a P1394b-compatible systemthough links. Typically, a cable is used for a link, as is provided forin the P1394b standard. However, any communication means may beemployed. By way of example, an infrared, RF, or other wireless systemmay be used, as well as an optical system.

Typically, a link is coupled to a node through a port. A port transmitsand receives messages and data between the node and link. As is known bythose of ordinary skill in the art, each node may have more than oneport.

FIG. 5 is a flowchart of a method for automatically healing a crossoveraccording to the present invention. FIG. 5 provides an excellentoverview of the present invention. The process begins with act 500 inwhich a node which wishes to connect to a bus listens for a connecttone.

As is appreciated by those of ordinary skill in the art, P1394bimplements a unique joining sequence that is triggered when a PHY ispowered up. When a PHY is powered up, it sends out a signal detect toneon the bus. When a PHY is on the bus and hears the signal detectoriginating from another PHY, the PHYs acknowledge each other and moveonto a connection detect stage, and eventually join each other on thebus.

Thus, in query 500 a PHY which wishes to connect to the bus is listeningfor the signal detect originating from another PHY. If the PHY receivesa tone, then the PHY is not suffering from a crossover and thereforemust be correctly coupled, and the process ends.

If the PHY does not receive a tone, then there is possibly a crossoverthat needs to be healed, and the process moves to query 502. In query502, the PHY examines a Boolean variable to see whether it shouldimplement a crossover. The Boolean variable is provided to prevent thecondition where two PHYs are attempting to heal a crossover at the sametime. Any means for generating a random true-false value may be employedin the present invention. In an exemplary non-limiting embodiment of thepresent invention, the random Boolean generator used for the root nodecontention algorithm in the P1394b is employed for the presentinvention.

If a false value is returned in query 502, then the process will returnto query 500 to see if it has received a tone. If a true value isreturned in query 502, then the process moves to act 504.

In act 504, the port will internally crossover its connection internallyby swapping TPA and TPB. The result of this is that, for the duration ofthe “cross-over healing”, the internal transmit logic of the port willuse TPA (instead of TPB) and the internal receive logic of the port willuse TPB (instead of TPA). Preferred methods for implementing a crossoveraccording to the present invention will be disclosed below.

After the crossover is accomplished in act 504, the process of FIG. 5repeats by moving back to query 500. If the crossover solved theproblem, then a tone should be heard in query 500, and the process ofFIG. 5 will end.

FIG. 6 is a flowchart of another aspect of the present invention. FIG. 6provides a more detailed embodiment which takes into accountcontingencies which may occur in actual practice.

In query 600, the PHY which wishes to join listens for a tone. This actis substantially similar to query 500 in FIG. 5, above. If the PHYreceives a tone, then the process of FIG. 6 ends, as there is nocrossover.

If the PHY does not receive a tone, then there is possibly a crossoverthat needs healing, and the process moves to query 602.

In query 602, the PHY will examine a random Boolean variable. This queryis substantially similar to query 502 in FIG. 5, above.

If the result of query 602 is false, then the process of FIG. 6 movesback to query 600 through connector A. If the result of query 602 istrue, then the process moves to query 604.

In query 604, the PHY determines whether it is still sending out a tone.As is appreciated by those of ordinary skill in the art, a PHY will sendout four tones in P1394b. It is desired that a PHY will not implement acrossover while it is still sending out a tone, as this would result infirst part of the tone being transmitted on one pair, and the remainingpart of the tone being transmitted on the other pair. Thus, if the PHYis still sending out tones in query 604, then the process will move toact 606 where the PHY will wait for a predetermined amount of time. Inan exemplary non-limiting embodiment of the present invention, the PHYwill wait in act 606 until it is finished sending out tones.

After the PHY has waited an appropriate amount of time in act 606, or ifthe PHY is not sending out tones and the result of query 604 isnegative, then the process moves to query 608.

Query 608 provides for a safe harbor in case tones have appeared whilethe PHY was working through the process of FIG. 6. In query 608, the PHYonce again checks to see whether it has received a tone. If the PHY hasreceived a tone, then there was no crossover in the first place, and theprocess of FIG. 6 ends.

If the PHY still has not received a tone, then there is possibly acrossover that requires healing, and the process moves to act 610.

In act 610, the PHY implements a crossover healing process substantiallysimilar to act 504 in FIG. 5. When the PHY has finished the crossoverhealing of act 610, the process of FIG. 6 will move back to query 600through connector A to see if the crossover has solved the problem. Ifthe crossover has solved the problem, the tone should be heard in query600, and the process of FIG. 6 will end. If not, the process of FIG. 6will repeat itself.

FIG. 7 is a schematic diagram of crossover logic according to thepresent invention. FIG. 7 shows a P1394b-compliant port 700 havingtransmit and receive logic standard in the art for implementing theP1394b standard.

FIG. 7 show the transmit logic couple to connection point TPB throughpassgate 706. Passgate 706, and all passgates shown in FIG. 7, may beimplemented through any means standard in the art, such as a standardparallel CMOS configuration, or a latch. The transmit logic is alsocoupled to connection point TPA through passgate 702.

The receive logic is coupled to connection point TPA through passgate704. The receive logic is also coupled to connection point TPB throughpassgate 708.

A crossover enable signal is provided to passgates 702 and 708. Aninverted crossover enable is provided to passgates 704 and 706. It iscontemplated that the crossover enable signal may be inverted throughany means standard in the art, such as an inverter. In a preferredembodiment of the present invention, the crossover enable signal and theinverted crossover enable signals are provided to the common gate oftheir respective passgates to provide a means for switching TPA and TPB.

In operation, the crossover enable signal is normally low. As can beseen by inspection of FIG. 7, a low crossover enable signal will couplethe receive logic to TPA through passgate 704 which will be on becauseof the low crossover enable signal being applied. The normally lowcrossover enable signal will also couple the transmit logic to TPBthrough passgate 706, which will be on by virtue of the low crossoverenable signal applied to it.

In a preferred embodiment of the present invention, the logical state ofthe crossover enable signal will be determined by the processesdisclosed in FIGS. 5 and 6. When the processes of FIGS. 5 and 6 resultin a crossover act being required, the crossover enable signal will bebrought high by circuitry on the PHY. This circuitry may be anycircuitry standard in the art for implementing the P1394b standard andis not shown in FIG. 7.

As can be seen by inspection of FIG. 7, when the crossover enable signalis brought high, passgates 702 and 708 will be turned on, and pass-gates704 and 706 will be turned off, thus coupling the receive logic toconnection point TPB and coupling the transmit logic to connection pointTPA.

Thus, the circuitry of FIG. 7, with the processes of FIGS. 5 and 6,provide a simple and effective means for automatically implementing acrossover and eliminates the need for patch cables, and allows the userto connect the system with many different types of patch cords withoutfear that the system will fail. Thus, with the advantages provided bythe present invention, a user may connect a P1394b-compliant system witha cable that employs an internal crossover, or a non-crossover patchcable, and the system will function regardless of which cable the useremploys.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art that manymore modifications than mentioned above are possible without departingfrom the inventive concepts herein. The invention, therefore, is not tobe restricted except in the spirit of the appended claims.

1. A data communication apparatus comprising: a transmit interfaceconfigured to transmit a first predetermined signal on power up; areceive interface configured to receive a second predetermined signal;the data communication apparatus configured to perform a crossoverfunction if the receive interface does not receive the secondpredetermined signal, the crossover function comprising: examining arandom value, the random value being determined by an algorithm, and ifthe value of the random value meets a predetermined criterion, then:configuring the transmit interface to receive the second predeterminedsignal; and configuring the receive interface to transmit the firstpredetermined signal; wherein the algorithm is also utilized for anotherpurpose within the data communication apparatus.
 2. The datacommunication apparatus of claim 1, wherein the another purposecomprises resolving contention between two or more nodes of a networkusing a serialized bus protocol.
 3. The data communication apparatus ofclaim 2, wherein the first predetermined signal comprises a signaldetect tone.
 4. The data communication apparatus of claim 3, wherein thesignal detect tone comprises a signal detect tone compliant with IEEEStd.1394b.
 5. The data communication apparatus of claim 4, wherein thesecond predetermined signal comprises a signal detect tone.
 6. The datacommunication apparatus of claim 5, wherein the second predeterminedsignal comprises a signal detect tone compliant with IEEE Std.1394b. 7.The data communication apparatus of claim 6, wherein the random valuecomprises a Boolean variable.
 8. The data communication apparatus ofclaim 7, wherein the predetermined criterion comprises a Boolean “true”value.
 9. The data communication apparatus of claim 8, wherein thecrossover function further comprises, if the value of the random valuedoes not meets a predetermined criterion, continuing listening for thesecond predetermined signal on the receive interface.
 10. Acommunication network comprising at least two nodes and a communicationbus, wherein: the at least two nodes communicate with each other overthe communication bus without an intervening crossover interface; and atleast one of the at least two nodes is configured for detection andhealing a crossover in communication, the detection and healingcomprising: detecting an absence of a first signal; determining whethera signal interface of the at least one of the at least two nodes isgenerating a second signal; and responsive to a probabilistic functionand the acts of detecting and determining, switching between a transmitport and a receive port.
 11. The communication network of claim 10,wherein the crossover interface comprises a cable, and the at least twonodes comprise nodes compliant with IEEE Std.1394b.
 12. Thecommunication network of claim 11, wherein the first signal comprises asignal detect tone compliant with IEEE Std.1394b.
 13. The communicationnetwork of claim 12, wherein the probabilistic function comprises aBoolean function.
 14. The communication network of claim 13, wherein theprobabilistic function is used by the at least two nodes for root nodedecision.
 15. The communication network of claim 14, wherein thedetection and healing further comprises transmitting a predeterminednumber of transmissions of a second signal.
 16. The communicationnetwork of claim 15, wherein the switching between the transmit port andthe receive port only occurs when the at least one of the at least twonodes is not generating the second signal.
 17. The communication networkof claim 16, wherein the predetermined number of transmissions is four(4).
 18. The communication network of claim 17, where the detection andhealing further comprises waiting, responsive to an outcome of thechecking, for a predetermined time period.
 19. The communication networkof claim 18, where the detection and healing further comprisesdetecting, after the predetermined time period, the first signal.
 20. Acommunication system, comprising: an interface comprising a firstcommunication path and a second communication path; and at least onenode including a logic circuit comprising a receive circuit and atransmit circuit; wherein: the transmit circuit is connected to a firstand a second communication paths via a first passgate, and the receivecircuit is connected to the first and the second communication paths viaa second passgate; the first passgate configured to, in combination witha crossover function and in response to a crossover enable signal,connect the transmit circuit either to the first communication path orthe second communication path; and the second passgate configured to, incombination with the crossover function and in response to the crossoverenable signal, connect the receive circuit either to the firstcommunication path or the second communication path; and wherein alogical state of the crossover enable signal is responsive to detectionof a signal on the second communication path and a value of a firstvariable, the value of the first variable being determined by analgorithm that is utilized for another purpose in addition to thecrossover function.
 21. The communication system of claim 20, whereinthe interface comprises a cable compliant with IEEE Std.1394b.
 22. Thecommunication system of claim 21, wherein the at least one nodecomprises a node compliant with IEEE Std.1394b.
 23. The communicationsystem of claim 22, wherein the interface comprises a cable having aninternal crossover.
 24. The communication system of claim 22, whereinthe interface comprises a non-crossover patch cable.
 25. Thecommunication system of claim 22, wherein the crossover enable signal isinverted before provision thereof to the second passgate.
 26. Thecommunication system of claim 22, wherein a logical state of thecrossover enable signal is changed in response to absence of a firstsignal on the first communication path.
 27. The communication system ofclaim 26, wherein the first signal comprises a tone signal compliantwith IEEE Std.1394b.
 28. The communication system of claim 27, whereinthe another purpose comprises resolving contention between the at leastone node and one or more other nodes of a network using a serialized busprotocol.
 29. A home network comprising at least two devices and acommunication bus, wherein: the communication bus comprises a firstsignal transmission path and a second signal transmission path; and atleast one of the at least two devices comprises a physical layerconfigured to detect reception of a signal on the second signaltransmission path; and if the physical layer has not received thesignal, then responsive to the lack of receipt of the signal examining avariable associated with a randomized function and implementing, by thephysical layer, a crossover process.
 30. A method of forming a networkcomprising: transmitting a first signal on a first interface; waitingfor a predetermined period of time after completion of the transmitting;checking at a second interface, after the predetermined period of timeis over after the transmitting, if a second signal is received; and ifthe second signal is received at the second interface, then attemptingto form a network; and if the second signal is not received at thesecond interface, and the first signal is determined not to betransmitted on the first or second interface at that time, thenperforming detection of the second signal on the first interface.
 31. Adata communication apparatus comprising: a first interface configured totransmit at least a first signal; a second interface configured toreceive at least a second signal; and logic in signal communication withthe first interface and the second interface, and configured to: waitfor a predetermined period after transmission of the first signal; andcheck the second interface, after the predetermined period has expired,to determine if the second signal is received; and wherein the logic isfurther configured to: if the second signal is received at the secondinterface, then attempt to form a network; and if the second signal isnot received at the second interface, and the first or second interfacesare not in use at that time, then perform detection of the second signalon the first interface.
 32. The data communication apparatus of claim31, wherein the first and second signals each comprise a signal detecttone.
 33. The data communication apparatus of claim 32, wherein thesignal detect tones comprise signal detect tones compliant with a highspeed serialized bus protocol.
 34. The data communication apparatus ofclaim 33, wherein the serialized protocol is compliant with at least oneversion of IEEE Std.1394.
 35. The data communication apparatus of claim31, wherein the first and second interfaces comprise interfacescompliant with a high speed serialized bus protocol.
 36. The datacommunication apparatus of claim 31, wherein the data communicationapparatus is configured to operate with both (i) a cable having nointernal crossover between first and second pathways associated with thefirst and second interfaces, respectively; and (ii) a cable having aninternal crossover between first and second pathways associated with thefirst and second interfaces, respectively.
 37. The data communicationapparatus of claim 31, wherein the apparatus is further configured totransmit said first signal upon power-up.
 38. A data communicationapparatus comprising: a first interface configured to transmit at leasta first signal; a second interface configured to receive at least asecond signal; and logic in signal communication with the firstinterface and the second interface, and configured to: check the secondinterface to determine if the second signal is received; if the secondsignal is received at the second interface, attempt to form a network;and if the second signal is not received at the second interface, andone or more of the first or second interfaces are in use at that time,then: (i) wait for a predetermined period; and (ii) after expiration ofthe period, perform detection of the second signal on the firstinterface.
 39. The data communication apparatus of claim 38, wherein thefirst and second signals each comprise a signal detect tone.
 40. Thedata communication apparatus of claim 39, wherein the signal detecttones comprise signal detect tones compliant with a high speedserialized bus protocol.
 41. The data communication apparatus of claim40, wherein the serialized protocol is compliant with at least oneversion of IEEE Std.1394.
 42. The data communication apparatus of claim31, wherein the first and second interfaces comprise interfacescompliant with a high speed serialized bus protocol.
 43. The datacommunication apparatus of claim 38, wherein the data communicationapparatus is configured to operate with both (i) a cable having nointernal crossover between first and second pathways associated with thefirst and second interfaces, respectively; and (ii) a cable having aninternal crossover between first and second pathways associated with thefirst and second interfaces, respectively.
 44. The data communicationapparatus of claim 38, wherein the apparatus is further configured totransmit said first signal upon power-up.